The ability of radiation therapy to achieve local-regional control of several types of cancer is currently limited because sterilizing doses in the range of 6000-7000 rads in 5-6 weeks cannot be delivered without serious complications from normal-tissue reactions. This situation can be improved by the development of radiation modalities which provide higher dose localization in the region of the tumor volume. Theoretical calculations as well as a pilot study by the authors have demonstrated that the application of magnetic fields to high-energy electron as they penetrate into the patient cause significant improvements in the dose distribution. This proposal is for the design and fabrication of a large superconducting magnet for the enhancement of dose distributions produced by electrons in the range of 10-60 MeV under conditions simulating those of clinical radiation therapy.